I favour the former where we don’t specify this information because I think it adds unnecessary noise to the name and is a detail about the implementation of the object behind that variable which I don’t care about when I’m reading the test.

I do care about it if I want to change something but if that’s the case then I can easily see that it’s a mock or stub by looking at the place where it’s instantiated.

From my experience we often tend to end up with the situation where the variable name suggests that something is a mock or stub and then it’s used in a different way: